The present invention relates to an apparatus and a method of reproducing moving pictures at a regular or a different reproduction speed. Particularly, this invention relates to an apparatus and a method of reproducing moving pictures as interlaced pictures at a variable speed.
Moving pictures are reproduced from storage media such as magnetic tapes and video discs at a regular reproduction speed that matches a rate of motion of the moving pictures or a variable speed.
Variable-speed reproduction includes reproduction at slow speeds such as still-picture reproduction and slow-motion reproduction in the range from 1/10 to ½× speed and also at high speeds such as 2× speed and frame search in the range from 5 to 50× speed. Reproduction at a speed, for example, two times higher than a regular speed is termed as 2× speed reproduction hereinafter.
One requirement of such variable-speed reproduction is to produce pictures the same as the regular-speed reproduction in quality. Therefore, slow-speed reproduction reproduces a picture twice or more in succession in accordance with a reproduction speed whereas high-speed reproduction decimates pictures in accordance with a reproduction speed to achieve the same picture rate, for example, 60 fields per second.
Each field exists per 1/60 seconds and even and odd fields are arranged alternately for moving pictures formed by interlaced scanning at the picture rate of 60 fields per second. This alternate field arrangements gives a normal relationship (parity) between the even and odd fields.
The normal parity will be often destroyed at variable-speed reproduction due to generation of a field twice or more in succession or field decimation, resulting in displaying reverse-parity fields.
Generation of reverse-parity fields will be discussed in detail.
A moving-picture signal is retrieved from a storage-medium at a retrieval speed in accordance with a reproduction speed.
In regular-speed reproduction, the retrieved moving-picture signal is reproduced as interlaced pictures and field pictures of regular interlaced pictures are output from the reproduced interlaced pictures in synchronism with output-format interlaced pictures.
In high-speed reproduction, however, some pictures are only reproduced from the retrieved moving-picture signal and decimated per field.
On the contrary, slow-motion reproduction reproduces all pictures from the retrieved moving-picture signal and outputs a field twice or more in succession at a speed in accordance with a reproduction speed slower than an actual picture speed.
FIG. 1 illustrates scanning lines in ½ and 2× speed reproduction in relation to regular-speed reproduction.
In FIG. 1, dot-line circles indicate scanning lines located at positions different from regular scanning lines at regular-speed reproduction. The regular scanning lines are indicated by circles. Their vertical positional replacements are indicated by arrows.
The dot-line-circle scanning lines in both high-speed reproduction and slow-motion reproduction have a reverse parity with the regular scanning lines at half fields.
Odd-times speed reproduction such as 3×, 5× and 7× speed reproduction have a normal parity but reproduce some picture components only due to inferior decoding performance, thus resulting in inappropriate filed pictures.
The reverse parity for interlaced pictures discussed above causes low image resolution, aliasing (image degradation with stepped oblique lines, etc) and vertical image vibration.
Reproduction-speed settings only for normal parity highly restrict the range of reproduction speed.